In recent years, battery packs utilizing lithium ion batteries have been used in portable apparatuses such as digital cameras. In general, it is arguably difficult to detect a remaining battery level based on the voltage level of a lithium ion battery. Because of this, a method of measuring a remaining battery level uses a microcomputer or the like to detect charge and discharge currents of a battery and to integrate the detected charge and discharge currents.
A fuel gauge IC for measuring a remaining battery level as described above includes an analog circuit such as a high-precision AD converter circuit and a digital circuit such as a timer and a CPU for integrating measured current values. Such an analog circuit and a digital circuit are implemented as a single-chip semiconductor integrated circuit device.
One example of the AD converter to convert an analog signal into a digital signal in the above-noted analog circuit is a delta-sigma AD converter circuit (see Patent Document 1, for example).